Recently, the recording density of optical disc media has been rapidly increasing. In the case of optical disc media allowing digital data recording, data recording, reproduction and management are generally performed in units of blocks, each block having a prescribed byte length. (Such a block will be referred to as a “data block”.) Each data block is given address information. Data recording and reproduction are performed with reference to the address information.
For recording data on an optical disc medium, user data such as, for example, audio, video and computer data to be stored is provided with redundant data such as, for example, an error correction code (parity code) used for detecting or correcting a data error when the stored data is read. The user data provided with the redundant data is transformed in accordance with a modulation code system suitable to the characteristics of recording and reproduction signals for the optical disc medium. On the optical disc medium, the post-transformation data bit stream is recorded. One known modulation code system which is often used for optical disc media is run length limited code.
A run length limited code determines the post-transformation data bit stream so that the number of “0” bits interposed between two “1” bits in a bit sequence is limited to a prescribed number. The number of “0” bits interposed between “1” bits will be referred to as a “zero run”. An interval (length) between one “1” bit to the next “1” bit in a data bit stream (code sequence) will be referred to as an “inversion interval”. The limitation of the zero run determines the limits, i.e., the maximum value and the minimum value, of the inversion interval of a data bit stream. The maximum value will be referred to as a “maximum inversion interval k” and a “minimum inversion interval d”.
In the case where a data bit stream is recorded on an optical disc medium by mark position recording (PPM: Pit Position Modulation), bit “1” of the data bit stream corresponds to a recording mark, and a zero run “0”s corresponds to a space. In the case where a data bit stream is recorded on an optical disc medium by mark length recording (PWM: Pulse Width Modulation), the recording state, i.e., whether a recording mark is to be recorded on the optical disc medium or a space is to be recorded, is switched when a “1” bit of the data bit stream occurs. In the case of mark length recording, the inversion interval corresponds to the length of a recording mark or the length of a space.
Accordingly, when, for example, the minimum value of the physical size of marks which can be formed on an optical disc medium (such a minimum value will be referred to as a “mark unit”) is equal in the mark position recording and the mark length recording, mark position recording requires 3 mark units in order to record data of a minimum code length (3 bits “100” of a data bit stream), but the mark length recording requires only one mark unit.
When a run length limited code having a minimum inversion interval d=2 is used, the number of bits per unit length of track of the optical disc medium is larger in the case of the mark length recording than in the case of the mark position recording. Namely, the recording density is higher by the mark length recording than by the mark position recording.
In general, when a data bit stream transformed into a modulation code is recorded on an optical disc medium, a synchronization pattern is often inserted into the data bit stream at every prescribed cycle of the data bit stream. Such a synchronization pattern performs proper data synchronization when the data bit stream is read. According to one known technique for inserting the synchronization pattern, a synchronization pattern including a sequence which does not exist in a modulation code sequence is inserted at the start of an area, referred to as a frame area, having a prescribed byte length.
Among some data formats for recording-type optical disc media which have recently been put into practice, the DVD-RW data format will be briefly described.
In the DVD-RW data format, address information is arranged by pre-pits which are located in a land between two adjacent groove tracks in which data is to be recorded. Data is continuously recorded on the groove tracks. An ECC block, which is a minimum unit for data recording and reproduction, includes a plurality of areas, referred to as data frame areas, each having a fixed byte length. A data frame area includes a synchronization information area provided at the start thereof and a data area. Data recording or reproduction is begun and terminated in the data area in the data frame area which is located at the start of each ECC block. An operation for additionally recording data in an ECC block next to the ECC block which has data already recorded therein is referred to as “linking”. A data frame area corresponding to a position at which data recording is begun and terminated is referred to as a “linking frame area”.
FIG. 44 shows a data format of a linking position and the vicinity thereof of a conventional DVD-RW. In a DVD-RW, one ECC block includes 16 sectors, and one sector includes 26 frame areas. The minimum unit for data recording is one ECC block. Data recording is begun and terminated at a data area DATA of a leading frame area (linking frame area) of a leading sector S0 of one ECC block. FIG. 44 shows the position at which data recording is begun and terminated as “start position of data recording”. In the example shown in FIG. 44, linking is performed so that the data recording is terminated at the 16th byte from the start of the linking frame area and the data recording is begun between the 15th byte and the 17th byte from the start of the linking frame area.
In the linking frame area in which the data recording is begun and terminated, data is recorded in a discontinuous manner. Therefore, data recorded from the linking beginning position (start position) to the next frame area cannot be read since accurate bit synchronization cannot be realized. Furthermore, when the low precision of linking causes the length of the frame area to be larger or smaller than the prescribed length, or when repeated linking recording in the same frame area degrades the signal in the frame area, signal reproduction systems for level-slicing, PLL or the like become unstable when the data recorded in and in the vicinity of the linking position is reproduced. In the worst case, there is a possibility that data cannot be read in several frame areas after the linking position. In such a case, error correction cannot be performed, which possibly generates a reading error. When the positioning accuracy when performing linking is less than one bit, the possibility of accurate data reading is increased. However, the tolerance of less than one bit is difficult to realize and thus is impractical as the recording density of data is increased.
The present invention, in light of the above-described problems, has an objective of providing a recording medium, a recording method, a reproduction method, a recording apparatus and a reproduction apparatus for allowing stable data recording and reproduction even at a beginning position and termination position of data recording.